Epoxide hydrolases are a group of enzymes that are ubiquitous in nature, detected in species ranging from plants to mammals. These enzymes are functionally related in that they catalyze the addition of water to an epoxide, resulting in a diol. One subtype of epoxide hydrolase is the soluble epoxide hydrolase (sEH). sEH plays an important role in the metabolism of lipid epoxides. Endogenous substrates of sEH include epoxyeicosatrienoic acids (EETs), which are effective regulators of blood pressure and inflammation.
The metabolism of arachidonic acid by cytochrome P450 monoxygenase leads to the formation of various biologically active eicosanoids, and is the primary route of EET synthesis. Three types of oxidative reactions are known to occur to the precursor eicosanoids, and one of these, olefin epoxidation (catalyzed by epoxygenases), produces EETs. Four important EET regioisomers are [5,6]-EET, [8,9]-EET, [11,12]-EET, and [14,15]-EET. These arachidonic acid derivatives function as lipid mediators in certain tissues, potentially through receptor-ligand interactions, and further, can be incorporated into tissue phospholipids (Bernstrom et al. 1992, J. Biol. Chem. 267:3686-3690).
Hypertension has been shown to result from an impairment of endothelium dependent vasodilation (Lind, et al., Blood Pressure, 9: 4-15 (2000)). In healthy individuals, endothelium derived hyperpolarizing factor, EDHF, hyperpolarizes vascular smooth muscle tissue resulting in endothelium-dependent relaxation. EETs are known to provoke signaling pathways which lead to cell membrane hyperpolarization, and therefore have been considered as a candidate EDHF. In vascular tissue, hyperpolarization by EETs results in increased coronary blood flow and improved recovery of myocardium from ischemia-reperfusion injury. (Wu et al., 272 J. Biol. Chem 12551 (1997); Oltman et al., 83 Circ. Res. 932 (1998)). Accordingly, EETs are predicted to be useful in the treatment of hypertension as well as ischemia-related damage and disease.
In addition to promoting vasodilation, EETs have also been shown to exhibit anti-inflammatory properties. For example, 11,12-EET can reduce inflammation by decreasing the expression of cytokine induced endothelial cell adhesion molecules (such as VCAM-1) (Node, et al., Science, 285: 1276-1279 (1999); Campbell, TIPS, 21: 125-127 (2000); Zeldin and Liao, TIPS, 21: 127-128 (2000)). Other studies have demonstrated that EETs can inhibit vascular inflammation by inhibiting NF-κB and 1κB, which prevents leukocyte adhesion to vascular cell walls. As such, EETs are also predicted to be useful in reducing inflammation and alleviating endothelial cell dysfunction (Kessler, et al., Circulation, 99: 1878-1884 (1999).
Hydrolysis of EETs by sEH converts the EETs to corresponding diols. Such diols have been shown to exhibit diminished vasodilatory and anti-inflammatory effects (Smith et al., 2005, Proc. Natl. Acad. Sci. USA. 102:2186-91; and Schmelzer et al., 2005, Proc. Natl. Acad. Sci. USA. 102:9772-7). As inhibition of sEH leads to accumulation of active EETs, such inhibition provides a novel approach to the treatment of hypertension and vascular inflammation (Chiamvimonvat et al., 2007, J. Cardiovasc. Pharmacol. 50:225-37). To date, the most successful sEH inhibitors reported are 1,3-disubstituted ureas. These urea-based inhibitors have been shown to treat hypertension and inflammatory diseases through inhibition of EET hydrolysis in several animal models. However, these inhibitors often suffer from poor solubility and bioavailability, which makes them less therapeutically efficient (Wolf et al., 2006, J. Med. Chem. 335:71-80). Therefore there remains a need for identifying new sEH inhibitors for therapeutic application.